On 7/22/2018 3:21 PM, Himanshu Jha wrote:
On Sat, Jul 21, 2018 at 08:45:34PM +0300, Daniel Baluta wrote:
On Sat, Jul 21, 2018 at 6:43 PM, Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:
On Sat, Jul 21, 2018 at 6:36 PM, Himanshu Jha
<himanshujha199640@xxxxxxxxx> wrote:
+ /* Look up table 1 for the possible gas range values */
+ u32 lookupTable1[16] = {2147483647u, 2147483647u, 2147483647u,
+ 2147483647u, 2147483647u, 2126008810u,
+ 2147483647u, 2130303777u, 2147483647u,
+ 2147483647u, 2143188679u, 2136746228u,
+ 2147483647u, 2126008810u, 2147483647u,
+ 2147483647u};
This one needs perhaps a bit of though, but...
+ /* Look up table 2 for the possible gas range values */
+ u32 lookupTable2[16] = {4096000000u, 2048000000u, 1024000000u,
+ 512000000u, 255744255u, 127110228u, 64000000u,
+ 32258064u, 16016016u, 8000000u, 4000000u,
+ 2000000u, 1000000u, 500000u, 250000u, 125000u};
...this one obviously just a not needed one. You may replace it with a
one constant and simple calculation to get either value (index from
value, or value from index).
Indeed this can be reduce to:
125.000 << (15 - idx).
The real question here is if we approximate 255.744.255u to 256.00.00u how
much different is the result. Being a gas sensor I think it is very
hard to appreciate.
We can go with this formula + adding a comment with the table with the
exact coefficients.
So, I have planned to use this 125000 << (15 - idx) equation with
approximating the array members.
About the difference in results we would get after approximating isn't
much of a problem IMHO because gas sensor is primarily used for IAQ, and
IAQ is relative to the resistance reading.
For eg:
Resistance(ohm) IAQ
value < 30K Very bad
30k < value < 50k worse
50k < value < 70k bad
...
..
so on..
So, what I simply imply is the scale will be adjusted and nothing else
changes, unlike if it had been pressure, temperature, humidity.
The IAQ implementation is userspace application suggesting
good/bad/ugly air quality.
And since we know David Frey is planning to use this sensor in his
product mangOH board.
So, David, how are you planning to use the gas sensing part in your
product ? RGB leds, buzzer, alarm ?
Thanks Andy for the suggestion :)
My understanding is that the Bosch BSEC (Bosch Sensortec Environmental
Cluster - https://www.bosch-sensortec.com/bst/products/all_products/bsec)
software calculates the indoor air quality (IAQ) which is presented in
the range of 0 to 500. BSEC is proprietary, pre-compiled static
library. I don't know how they derive the IAQ, but it seems that it
could be based on smoothing outlying gas resistance values and
integrating other values such as temperature, humidity and pressure.
Unless this driver can somehow produce IAQ values of equal or greater
reliability to the BSEC library, then I would prefer that it just
present the raw gas resistance value so that a user can write a program
to feed the sensor data into BSEC.
mangOH isn't really a traditional product. It's an open hardware board
designed around Sierra Wireless cellular modules that run Linux. So I
don't have any specific use case in mind, but I want to enable our users
(and thus future products) to make use of air quality measurements.
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